The present invention relates to an electrophotographic photoreceptor, particularly to a novel electrophotographic photoreceptor having a light-sensitive layer containing an azo pigment and more particularly to an electrophotographic photoreceptor high in sensitivity and excellent in endurance against repeated use.
Hitherto, as electrophotographic photoreceptors, there have been widely known those which have a light-sensitive layer mainly composed of inorganic photoconductors such as selenium, cadmium sulfide, zinc oxide and silicon. However, these inorganic photoconductors are not necessarily satisfactory in sensitivity, heat stability, moisture resistance and endurance, and especially, selenium and cadmium sulfide suffer from the restriction in production and handling owing to their toxicity.
On the other hand, electrophotogrpahic photoreceptors having a light-sensitive layer mainly composed of organic photoconductive compounds have many advantages, namely, they are relatively easy in production, low in price, easy in handling and superior in heat stability to the selenium photoreceptors and they have recently been noticed.
As the organic photoconductive compounds, poly-N-vinylcarbazole is well known and an electrophotographic photoreceptor having a light-sensitive layer mainly composed of a charge transfer complex formed from the poly-N-vinylcarbazole and a Lewis acid such as 2,4,7-trinitro-9-fluorenone is disclosed in Japanese Patent Kokoku No. 50-10496. However, this photoreceptor is not necessarily satisfactory in sensitivity, film-formability and endurance.
On the other hand, function-separated photoreceptors of double-layered or dispersed type in which the carrier generation function and the carrier transport function are allotted to separate materials, respectively, have the merits that materials for the respective functions can be selected from a wide variety of materials and photoreceptors having optional characteristics such as chargeability, sensitivity and endurance can be relatively easily produced.
Hitherto, various materials have been proposed as the carrier generation materials and the carrier transport materials. For example, electrophotographic photoreceptors having a light-sensitive layer composed of combination of a carrier generation layer comprising amorphous selenium and a carrier transport layer mainly composed of poly-N-vinylcarbazole have been put to practical use. However, the carrier generation layer comprising amorphous selenium is inferior in endurance.
Furthermore, use of organic dyes or pigments as carrier generation materials has been proposed and, for example, electrophotographic photoreceptors containing monoazo pigments and bisazo pigments in the light-sensitive layer are proposed in Japanese Patent Kokoku Nos. 48-30513 and 56-11945 and Japanese Patent Kokai Nos. 52-4241 and 54-46558.
There have been proposed various electrophotographic photoreceptors containing low molecular weight organic photoconductors comprising combination of the above carrier generation materials with the carrier transport materials represented by triphenylamines, stilbenes and hydrazones and use of photoreceptors mainly composed of such organic photoconductive compounds is becoming widespread in the fields of electrostatic copying machines and photo printers.
However, for these copying machines and printers are required more and more higher speed output as well as higher function and the conventional photoreceptors do not have photo-sensitivity and photo-responsivity which satisfy these requirements. Moreover, when an organic photoreceptor is subjected to the complicated process which comprises charging, exposing and discharging in the copying machine, etc., the compounds constituting the photoreceptor not only perform the generation and transportation of carriers, but also receive stimuli such as ozone and light in a high electric field. Therefore, as the process is repeated, there occur various problems such as decrease of initial potential after charging and increase of residual potential after discharging.